Aeration apparatus are utilized in the treatment of water for the purpose of increasing the dissolved oxygen (DO) content of the water. A certain amount of dissolved oxygen is required for the life of fish and other aquatic organisms. Dissolved oxygen is also required to prevent the formation of offensive odors and to break down organic matter in water. The biochemical oxygen demand (BOD) is the measure of the amount of oxygen consumed in the biological processes which break down organic matter in water. A high BOD indicates that large amounts of organic waste are present and will use up large amounts of dissolved oxygen. Aeration apparatus are especially useful in increasing the amount of dissolved oxygen and, hence, are useful in high-BOD situations.
Aerators utilized in waste water treatment can be broadly classified into two types: a diffused air type, and a mechanical type. A diffused air type aerator introduces air or pure oxygen into water via submerged porous diffusers or nozzles. Mechanical type aerators agitate the water so as to promote solution of air from the atmosphere.
Mechanical type aerators are further classified as either surface aerators or turbine aerators. A surface aerator utilizes a submerged or partially submerged impeller which agitates the water vigorously to thereby entrain air in the water and cause a rapid change in the air-water interface. Turbine aerators generally utilize a rotating impeller which is disposed a certain distance below the surface of the water being treated. A draft tube is supported generally coaxial with the axis of rotation of the impeller and is utilized to supply air to the liquid adjacent the impeller.
In U.S. Pat. No. 3,465,706 to Gwidt, an apparatus for injecting air into the underwater exhaust of outboard motors is disclosed. Air is injected into water through a hollow propeller tube upon which a marine-type propeller is attached. A diffuser assembly comprised of a air of U-shaped and crossed plates is attached at the outlet end of the propeller tube. The air outlet end is disposed relatively close to the marine prop and the diffuser plates have a relatively narrow width. A round disc is attached to this lower end of the plates. The round disc would apparently inhibit axial flow of water and air bubbles.